1. Field of the Invention
The present invention relates to a method of producing an anti-corrosion member and an anti-corrosion member.
2. Description of Related Art
In accordance with an enlargement of memory storage in super LSI, a micro-fabrication technique is improved more and more, and a process which requires a chemical reaction is improved accordingly. Particularly, in a semiconductor manufacturing apparatus which requires a super clean condition, use is made of a corrosion gas of halogen series such as chlorine gas, fluorine gas and so on as a deposition gas, an etching gas and a cleaning gas.
For example, in the semiconductor manufacturing apparatus such as a thermal CVD apparatus, use is made of a semiconductor cleaning gas made of a corrosion gas of halogen series such as ClF3, NF3, CF4, HF and HCl after a deposition operation. Moreover, even in the deposition operation, use is made of a corrosion gas of halogen series such as WF6, SiH2Cl as a film forming gas.
Members constructing the semiconductor manufacturing apparatus are formed, for example, by anodized aluminum, aluminum nitride and so on.
Recently, it is found that silicon carbide (SiC) shows a relatively high anti-corrosion property with respect to the corrosion gas of halogen series mentioned above, and thus SiC is gradually used for the construction members of the semiconductor manufacturing apparatus.
Further, Japanese Patent Laid-Open Publication No.2-263972 (JP-A-2-263972) discloses a technique such that a fluorine passivated film made of a metal fluoride as a main ingredient in a stoichiometric state is formed on a surface of a metal member and an anti-corrosion property of the metal member with respect to the corrosion gas of halogen series is improved by the thus formed fluorine passivated film.
However, in the anodized aluminum, a surface oxidization film is shrunk at a temperature about 300xc2x0 C. and thus cracks are generated. Therefore, if it is exposed in the corrosion gas of halogen series at a high temperature, a base aluminum is corroded via crack portions, and the surface oxidization film corresponding to the thus corroded portion is peeled off from the member to generate particles.
Moreover, in aluminum nitride, there is a tendency such that use is made of a highly corrosion gas such as NF3 for the purpose of increasing an etching speed. Therefore, there is a drawback such that, if it is exposed in this highly corrosive gas at a high temperature, as in the case of anodized aluminum, a surface thereof is corroded and particles are generated. If the thus generated particles are sedimented on a base member provided in a semiconductor manufacturing apparatus, there occurs a phenomenon such as an insulation defect and a conduction defect, and these defects become a cause of a semiconductor defect.
Further, as mentioned above, silicon carbide shows a relatively high anti-corrosion property with respect to the corrosion gas of halogen series, but there is a drawback such that it is difficult to make a large construction member by using silicon carbide since it is hard to be sintered.
Here, there is a trial such that a porous member made of silicon carbide is formed, and then aluminum and so on are immersed in pores of the thus formed porous member to manufacture a large construction member. However, since an anti-corrosion property of the thus immersed aluminum is low, the thus manufactured large construction member has also a low anti-corrosion property with respect to the corrosion gas of halogen series, so that there is a drawback such that applicable fields of the thus manufactured large construction member are limited.
Further, in the method disclosed in JP-A-2-263972, there is a drawback such that an anti-corrosion property with respect to a plasma gas of halogen series especially with respect to a chlorine plasma gas is extremely low.
An object of the invention is to provide a new method of producing an anti-corrosion member and an anti-corrosion member which shows a high anti-corrosion property with respect to a corrosion gas of halogen series.
According to the invention, a method of producing all anti-corrosion member having a base member made of a metal in which aluminum is included, ceramics in which an aluminum element is included, or a composition member constructed by a metal in which aluminum and ceramics are included, and an anti-corrosion film formed on the base member, comprises the steps of: setting the base member in a container in which a solid fluorine compound is filled; heating the container at a temperature higher than a decomposition temperature of the fluorine compound to generate a decomposed gas of the fluorine compound and to subject the base member to a heat treatment with the decomposed gas of the fluorine compound; and forming an anti-corrosion film made of a fluoride on a surface of the base member.
Moreover, according to the invention, an anti-corrosion member comprises a base member made of a metal in which aluminum is included, ceramics in which an aluminum element is included or a composite member constructed by a metal in which aluminum and ceramics are included, and an anti-corrosion film made of a fluoride generated on a surface of the base member by setting the base member in a container in which a solid fluorine compound is filled and by heating the container at a temperature higher than a decomposition temperature of the solid fluorine compound.
The inventors attempted to find a new method of producing an anti-corrosion member and a new anti-corrosion member so as to improve an anti-corrosion property of a member which constructs a semiconductor manufacturing apparatus with respect to a corrosion gas of halogen series especially a plasma gas of halogen series.
As a result, it was found that a fluoride layer preferably having a main crystal phase of AlF3 was formed on a surface of a base member by setting the base member made of aluminum in a sealed container in which a solid fluorine compound such as NaHF2 is included and by heating the sealed container at a temperature higher than a decomposition temperature of the fluorine compound to perform a heat treatment for a predetermined time interval. Then, it was found that the thus formed anti-corrosion member had a high anti-corrosion property with respect to the corrosion gas of halogen series, especially the plasma gas of halogen series such as a chlorine plasma gas.
The base member mentioned above is formed by aluminum metal, an aluminum alloy, ceramic material in which an aluminum element is included, and a composite member. Therefore, it is possible to easily perform casting and sintering operations, and thus a manufacturing of the large construction member becomes easy.
Therefore, the anti-corrosion member manufactured according to the method of the invention has an excellent anti-corrosion property with respect to the corrosive gas of halogen series, and it is possible to easily manufacture the large construction member by using this anti-corrosion member. In addition, it is not necessary to use complicated manufacturing equipment, and thus problems associated with high cost manufacturing operations are limited.
FIG. 1 is a schematic view showing an X-ray diffraction pattern of an anti-corrosion member according to the invention. Moreover, FIG. 2 is an SEM cross sectional photograph showing a surface of the anti-corrosion member mentioned above.
From the X-ray diffraction pattern shown in FIG. 1, it is possible to observe a peak from AlF3 crystal phase other than a peak from aluminum which constructs the base member. That is to say, it is understood that a fluoride in which AlF3 is included as a main crystal phase is formed on a surface of the member obtained according to the method of the invention.
Moreover, from the SEM cross sectional photograph shown in FIG. 2, it is understood that a film having a layer a thickness of which is about 4 xcexcm is formed.
In the producing method according to the invention, a mechanism of forming a fluoride phase on a surface of the base member is assumed as follows.
For example, when a container, in which NaHF2 is filled as a solid fluorine compound, is heated and NaHF2 is heated at a temperature higher than a predetermined temperature, NaHF2 is decomposed by heat to generate hydrogen fluoride (HF) as shown in the following formula (1).
NaHF2xe2x86x92NaF+HFxe2x80x83xe2x80x83(1)
At the same time, an alumina (Al2O3) passivated film is formed on a surface made of, for example, an aluminum metal. Then, the thus formed alumina passivated film is reacted with the HF mentioned above according to the following formula (2), and alumina is transformed into aluminum trifluoride (AlF3). In this manner, a fluoride layer is formed on a surface of the base member.
Al2O3+6HFxe2x86x922AlF3+3H2Oxe2x80x83xe2x80x83(2)
It should be noted that the fluoride layer according to the invention is not necessarily existed as a complete continuous layer, but includes the case such that fluoride particles are aligned thickly.
In a method of producing an anti-corrosion member according to the invention, it is necessary to subject a base member made of aluminum metal and so on to a heat treatment with a decomposed gas of a solid fluorine compound.
This heat treatment can be performed under an atmosphere by using an open container, but it is preferred that this heat treatment is performed under a pressurized state by using a sealed container. In this manner, it is possible to produce an anti-corrosion member having an extremely high corrosion property with respect to a corrosion gas of halogen series, especially a plasma gas of halogen series such as a chlorine plasma gas.
In the case that the heat treatment is performed under a pressurized state, it is preferred to set a pressure larger than 1.5 atm (for the same reason as mentioned above), and it is further preferred to set a pressure larger than 5 atm. Moreover, in the case that the heat treatment is performed under a pressurized state, an upper limit of the pressure is preferred to be 20 atm and is further preferred to be 10 atm if taking into consideration of a withstanding pressure of the container.
A temperature of the heat treatment is not limited, the only limitation is that the temperature be higher than a decomposition temperature of a solid fluorine compound, thereby making it possible to generate a decomposed gas by decomposing the fluorine compound.
However, in order to obtain the anti-corrosion member having a high anti-corrosion property with respect to the plasma gas of halogen series by subjecting the base member to the heat treatment under a pressurized state mentioned above, it is preferred to perform the heat treatment at a temperature 0-200xc2x0 C. higher than the decomposition temperature of the solid fluorine compound, and it is further preferred to perform the heat treatment at a temperature more than 10xc2x0 C. higher but at maximum 150xc2x0 C. higher.
Moreover, a time interval of the heat treatment is varied in accordance with a thickness of a fluoride layer to be formed, a pressure in the container and kinds of fluorine gases, but it is preferred to be 5-40 hours.
Further, the solid fluorine compound used in this invention is not limited. All that is required is that it has a specific decomposition temperature and generate a decomposed gas by heating it at a temperature higher than the decomposition temperature. However, it is preferred to use the solid fluorine compound having the decomposition temperature of 100-300xc2x0 C. If the solid fluorine compound has a relatively low decomposition temperature mentioned above, it is possible to easily heat the container during the heat treatment. Moreover, it is possible to easily perform the heat treatment of the base member under a pressurized state. As the solid fluorine compound, use is made of NaHF2, KHF2 and NH4HF2, decomposition temperatures of which are 140-160xc2x0 C., 240xc2x0 C. and 120-160xc2x0 C., respectively. Moreover, it is particularly preferred to use a fluorine compound which includes no metal element, and also it is particularly preferred to use the fluorine compound which generates hydrogen fluoride by the decomposition. Among them, it is most preferred to use NH4HF2. A meaning of the solid fluorine compound includes a bulk type, a particle type and a powder type. Since the solid fluorine compound of the powder type has a large surface area, it is possible to make a temperature of the overall powders uniform in a relatively short time, and thus it is possible to easily generate the decomposed gas by the decomposition.
In the producing method according to the invention, as the base member which constructs the anti-corrosion member, use is made of the following materials.
(1) metal in which aluminum is included: use is made of pure aluminum metal or aluminum alloy. The aluminum alloy may include silicon, iron, titanium, copper, manganese, magnesium, chromium and zinc other than aluminum. Particularly, it is preferred to use Alxe2x80x94Si alloy, Alxe2x80x94Mg alloy, Alxe2x80x94Cuxe2x80x94Mg alloy and Alxe2x80x94Sixe2x80x94Mg alloy. Moreover, it is also particularly preferred to use the aluminum alloy which includes magnesium.
(2) ceramics in which an aluminum element is included: it is particularly preferred to use aluminum nitride and alumina.
(3) composition member constructed by metal in which aluminum and ceramics are included: use is preferably made of the above-mentioned metal in which aluminum is included. The above-mentioned ceramics are not limited, but it is particularly preferred to use ceramics in which an aluminum element is included.
If use is made of a metal in which aluminum is included or a composition member, it is possible to easily form the base member having a predetermined dimension and shape. Therefore, the producing method according to the invention can be applied to the base member having a large dimension or the base member having a specific shape, and thus it is possible to easily form the anti-corrosion member having a large dimension or the anti-corrosion member having a specific shape. As a result, the producing method according to the invention can be applied to wide applications such as a semiconductor manufacturing apparatus.
The anti-corrosion member according to the invention is remarkable since it has an extremely high corrosion property with respect to chlorine plasma gas in addition to fluorine plasma gas. A weight loss of the anti-corrosion member is preferred to be smaller than 15 mg/cm2 and is further preferred to be smaller than 1 mg/cm2 when it is exposed at 460xc2x0 C. for 5 hours in chlorine plasma gas obtained by exciting at a high frequency of 13.56 MHz and 800 W.
Therefore, in the case that the anti-corrosion member having the properties mentioned above is used for the semiconductor manufacturing apparatus as one example, it is possible to use the anti-corrosion member for a sufficiently long time interval under a normal condition as compared with known materials.
Moreover, according to the invention, a method of producing an anti-corrosion member having a base member made of a metal in which aluminum is included and an anti-corrosion film formed on the base member, comprises the steps of: setting the base member in a container in which a solid fluorine compound is filled; heating the container at a temperature higher than a decomposition temperature of the fluorine compound to generate a decomposed gas of the fluorine compound and to subject the base member to a heat treatment with the decomposed gas of the fluorine compound, so that an intermediate film made of a fluoride is formed on a surface of the base member; subjecting the base member and the intermediate film to a heat treatment to react with each other; and forming an anti-corrosion film made of a fluoride.
The inventors found that a fluoride film, which did not obtain a sufficient anti-corrosion property with respect to the corrosion gas of halogen series and which was easily peeled off from a surface of the base member, was generated on a surface of the base member, when various conditions such as the kind of fluorine compound, temperature and pressure were varied during the fluoridizing of the base member made of the metal in which aluminum was included. Then, it was understood that if such a fluoride film was further subjected to a heat treatment at a high temperature, the fluoride was reacted with a surface of the base member, and thus the fluoride film having a high anti-corrosion property was generated. The intermediate film made of fluoride having no anti-corrosion property mentioned above has an appearance, for example, shown in FIG. 3. Moreover, the film obtained by subjecting the intermediate film to heat treatment has an appearance shown in FIG. 4.
The inventors investigated characteristics and anti-corrosion property of the thus finally obtained fluoride anti-corrosion film and found that it had remarkable features as follows.
That is to say, as shown in FIGS. 5, 6, 10 and 11 for example, the anti-corrosion film was formed by fluoride particles which cover a surface of the base member. The fluoride particles have a large particle size, and when a line is drawn on a surface of the anti-corrosion film, the number of boundary phases across the line is smaller than 100 and larger than 5 per the line having a length of 10 xcexcm on an average. This definition corresponds to a particle size of 0.1 xcexcM-2.0 xcexcm.
The fluoride film, generated by contacting the fluoride gas to the metal in which aluminum is include or by contacting the decomposed gas of the solid fluorine compound mentioned above, is very fine since it is obtained by means of a vapor method, and particles of the fluoride film are not distinctly observed by a microscope having 5000 magnification. On the contrary, the thus obtained anti-corrosion film has the features such that a particle size is very large, particles are thickly contacted with each other and there is no boundary phase.
Moreover, the fluoride particles include at least one (preferably both) of aluminum fluoride phase and magnesium fluoride phase. An aluminum element and a magnesium element are transferred from a surface of the base member to the film.
A thickness of the anti-corrosion film is assumed to be 0.1-2.0 xcexcm in a normal condition since it is not observed by an SEM microscope having 5000 magnification.
An atmosphere during the heat treatment of the base member and the intermediate film is not limited if only it affects the base member, but it is particularly preferred to use an atmosphere in which oxygen and inert gas are included. A temperature of the heat treatment is preferred to be higher than 200xc2x0 C. from the view point of improving the reaction between the intermediate film and the base member, and it is further preferred to be higher than 300xc2x0 C. Moreover, in order to prevent a deterioration of the base member, it is preferred to be lower than 650xc2x0 C. and is further preferred to be lower than 600xc2x0 C.
The solid fluorine compound which is accommodated in the container is preferred to be the fluorine compound including no metal element. Such a fluorine compound is not limited if only it can be decomposed, but it is particularly preferred to be NH4HF2.
The intermediate film is generated by the reaction between the base member and fluoride gas, and it is particularly preferred to be an aluminum fluoride ammonium film.
Moreover, the inventors found that it was generally possible to generate an anti-corrosion film made of a fluoride by heating the base member and aluminum fluoride ammonium to react with each other.
That is to say, as mentioned above, the aluminum fluoride ammonium film is firstly generated as the intermediate film by heating the solid fluorine compound and the base member in the container. Then, the base member and the aluminum fluoride ammonium film are subjected to the heat treatment mentioned above in the container to generate the anti-corrosion film.
Moreover, as another method, it is possible to perform the heat treatment under a condition such that powders of aluminum fluoride ammonium are contacted to a surface of the base member. The powders mentioned above can be generated by a chemical reaction for example between aluminum hydroxide and ammonium fluoride saturated solution.
In this case, the aluminum fluoride ammonium powders are further accommodated in the container, and the base member is embedded in the powders. Then, the heat treatment is performed under the condition mentioned above. In another case, a formed film is obtained by mixing the aluminum fluoride ammonium powders with suitable organic solvent, binder and so on, preparing a coating slurry, and coating the coating slurry on the base member. The thus obtained formed film is subjected to the heat treatment together with the base member.
Here, the aluminum fluoride ammonium may be made of (NH4)3AlF6 crystal only. Moreover, aluminum element of (NH4)3AlF6 crystal may be substituted by other metal elements if only (NH4)3AlF6 crystal maintains its crystal structure. As the other metal elements, it is generally preferred to use metal elements which are included in an aluminum alloy. As such metal elements, it is preferred to use silicon, magnesium, manganese, copper, iron and so on. Particularly, in an application of semiconductor manufacturing it is preferred to use silicon or magnesium.
The anti-corrosion member according to the invention can be applied to suscepter which is heated by means of an infrared lamp, heater for heating a semiconductor, suscepter provided on a heating surface of an heater for heating a semiconductor, suscepter in which an electrode for a static chuck is embedded, suscepter in which an electrode for a static chuck and a resistance heater are embedded, and suscepter in which an electrode for a high frequency plasma generation and a resistance heater are embedded. Moreover, the anti-corrosion member according to the invention can be used as the base member of the semiconductor manufacturing apparatus such as dummy wafer, shadow ring, tube for generating a high frequency plasma, dome for generating a high frequency plasma, high frequency transmitting window, infrared transmitting window, lift pin for supporting a semiconductor wafer, shadow plate and so on.